[Structural similarity and signal transduction of cytokine receptors]

The advent of expression cloning has established a new group of membrane glycoproteins, called the cytokine receptor superfamily. Members of this family have common structural similarities in the extracellular region and no intrinsic tyrosine kinase activity is seen in the intracellular region. A combination of two distinct subunits (alpha and beta) in the family has been shown to generate high-affinity receptors in which the alpha subunits specify the binding and the beta subunits function as transducers that are presumably associated with tyrosine kinases. The high-affinity receptors for IL-3, IL-5 and GM-CSF all share the same beta subunit. The high-affinity receptor for IL-2 is however unique in that it requires a third component, notably, the gamma subunit, whose gene we have recently cloned.